FR2690224A1 - Steam generator equipped with an advanced deflection and purge device. - Google Patents

Abstract

In a steam generator equipping a nuclear power station and comprising inverted U-shaped tubes connected to a tube plate (12) and surrounded by an inner casing (26) housing a lower flow distribution plate (41) in its lower part, the space (46) called "water street" between the tube plate (12), the flow distribution plate (41) and the hot and cold branches of the tubes contains a deflection and purge box (44) . This box (44) extends over the entire length of the water street and, in height, up to near the upper edge of the inner casing (26). It is provided on its underside with purge orifices (50) and fulfills both a deflection function and a secondary fluid drainage function near the tube plate (12).

Description

STEAM GENERATOR PROVIDED WITH A DEVICE

  DEFLECTION AND PERFECTED PURGE.

DESCRIPTION

  The invention relates to a steam generator designed to be used in a pressurized water nuclear reactor and of which the secondary part is equipped,

  in the immediate vicinity of the tube plate, a device

  original design deflection and purge.

  As illustrated in particular by document FR-A-

  2,333,200, a steam generator fitted to a power plant

  nuclear usually includes an outer shell

  upper, of vertical axis, whose interior space is divided into two parts, in the direction of the height, by a horizontal plate called "plaque à tubes" (in English, "tube sheet") The ends of the tubes a bundle of inverted U tubes are attached to the

  tube plate and open below it

  pectively in an intake manifold and in a

  collector for discharging the water circulating in the

  primary reactor boil, called "primary water".

  The water circulating in the secondary circuit of the steam generator, called "secondary water" is a mixture of water

  known as "drinking water" from outside the general

  steam and water generator known as "recirculated water from the upper part of the steam generator Food water" is injected into the part of the steam generator located above the tube plate by a feed distributor , toroidal or

  semi-toric This power distributor is

  tuément placed above an annular recirculation space formed between the outer envelope and an inner envelope covering the bundle of tubes and whose lower edge is spaced from the tube plate.

  In such a steam generator, it is essential

  tial to prevent as much as possible the stagnation of the secondary water in certain zones adjacent to the tube plate In fact, this water can contain sludges whose deposition on the tube plate, around the tubes of the bundle, can lead to rapid corrosion of these tubes necessitating their sealing When too many tubes of the steam generator

  becomes inoperative, it is necessary to replace

  place the steam generator as a whole This is obviously not desirable as well from the point

  of cost only in terms of downtime

  stabilization of the resulting nuclear power plant.

  In particular to limit these areas of stagnation

  tion of secondary water near the tube plate, usually in the lower part of the surrounding inner envelope, the tube bundle, a lower horizontal distribution plate

  with an opening in its central part

  trale. Another problem which arises in the area of the steam generator located immediately above the tube plate relates to the homogenization of the

  temperature of the mixture between the drinking water introduced

  te in the generator by its supply manifold and the recirculation water from the water / steam separators placed in the upper part of the generator and

  which descends through the annular recirculation space.

  It is also desirable to ensure good regulation.

  tion of the flows of this mixture before it rises

  in the inner envelope around the tubes of the

  ceau. This problem is generally solved by placing on the tube plate, in the space, usually called "water street", formed between this plate, the plate

  flow distribution and hot and cold branches

  tubes of the deflector devices in the form of

  profiles (in English, "tube lane blocking device").

  In addition, it is also desirable to provide a drain immediately above the tube plate, in order to allow a withdrawal of the secondary fluid in this zone and to purge mainly in the zones where the flow of the secondary fluid takes place at lower speed, especially in the center

from the tube plate.

  To fulfill this function, we usually have

  in the water street two pipes pierced with holes in the lower part and connected to a circuit

  outside the steam generator.

  This purge circuit makes it possible to check the concentra-

  chemical reactions of the secondary fluid, in order to

  stick to acceptable values It also allows the suspension of suspended matter contained in

  the secondary fluid near the tube plate.

  By way of example, document US-A-4 664 178 describes a steam generator equipped with purge piping near the tube plate and comprising L-shaped deflection means mounted above the drain piping, at the base of the casing

  interior covering the bundle of tubes.

  If the deflection and purge devices

  used so far function satisfactorily

  health, they have the disadvantage of requiring the addition inside the steam generator of a relatively large number of separate parts, which complicates the assembly of the generator, increases

  the cost price and complicates maintenance.

  The object of the invention is precisely a general

  steam generator with inverted U-shaped tubes, comprising deflection and purging means of a new type,

  consist of a single structure filling simultaneously-

these two functions.

  More specifically, it is proposed to conform

  mention to the invention a steam generator comprising

  both: an outer envelope, with a vertical axis; a horizontal tube plate tightly fixed inside the outer casing;

  a bundle of inverted U-shaped tubes comprising branches

  hot ches and cold branches having extremi-

  tees fixed on the tube plate and opening below it, respectively in a

  intake manifold and in an exhaust manifold

  cuation of primary fluid; an inner envelope covering the bundle of tubes, a lower edge of which is spaced from the tube plate,

  and forming with the outer envelope an annu-

  recirculation area; secondary water supply means opening into the outer casing, above the tube plate;

  secondary steam extraction means through

  towards upper parts of the inner and outer envelopes; and deflection and purging means placed in a space formed between the tube plate, the first horizontal plate and the hot branches and the cold branches of the tubes; characterized by the fact that the deflection means and

  purge valve include one (or more) deflection box

  tion and purge which extends over all (or part

  de) the length of said space, up to near the enti-

  inner velvet, and which extends in height up to near the lower edge of the inner envelope,

  said box being spaced from the tube plate and pre-

  feeling bleed holes next to it

niere.

  Preferably, the deflection and purge box extends in height up to an intermediate level

  between the flow distribution plate and the bottom edge

  laughter of the inner envelope In addition, manholes formed in the latter as well as in the outer envelope of the steam generator open immediately above the longitudinal ends

  the deflection and purge box.

  The deflection and purge box according to the invention is connected to drainage means by at least one drainage tube which opens at at least one of the ends of the box, at the bottom of the latter.

  In a preferred embodiment of the invention,

  vention, at least two drainage tubes open laterally in a central part of the deflection and purge box, on either side of this box, which has orifices facing the tube plate This characteristic makes it possible to improve the drainage efficiency in the central part of the steam generator located immediately above

from the tube plate.

  According to a preferred embodiment of the in-

  vention, the deflection and purge box has

  a bottom forming a longitudinal recovery groove

  in which open the bleed orifices.

  Depending on the case, the deflection and drain box can have a uniform cross section

  over its entire length or on the contrary evolutive.

  The invention applies equally to all

  type of tube plate steam generators and in particular

  ment to "boiler" type steam generators, as to "axial preheater" type steam generators. More specifically, in the case of generators

  "boiler" type steam, devoid of any separation

  ration between the hot and cold branches of the tubes, the deflection and purge box rests on the tube plate by means of support studs between

  which are formed the drain holes.

  Furthermore, in steam generators of the "axial preheater" type, a vertical separation plate is placed between the hot and cold branches of the bundle tubes and connected to the tube plate In this case, the deflection and purge box includes two parts located on either side of

  the separation plate and supported by this plate.

  We will now describe, by way of examples not

  limiting, two preferred embodiments of the invention

  tion, with reference to the accompanying drawings, in which: Figure 1 is a side view illustrating

  schematically, in partial vertical section, a general

  steam generator of boiler type produced in accordance with the invention; Figure 2 is a horizontal sectional view

  on a larger scale along line II-II of the figure

  re 1; Figure 3 is an enlarged sectional view along line III-III of Figure 2; Figure 4 is a sectional view along line IV-IV of Figure 3; Figure 5 is a sectional view comparable to Figure 4 illustrating a second embodiment of the invention, in the case of a steam generator of the axial preheater type; and

  FIG. 6 is an enlarged perspective view

  chée representing the deflection and purge box

illustrated in figure 5.

  In Figure 1, there is shown schematically-

  an illusor-type steam generator

  trant a first possible embodiment of the

  vention This steam generator is designed to transfer heat between the primary water circuit and the secondary water / steam circuit of a reactor

pressurized water nuclear.

  In FIG. 1, the reference 10 designates the outer envelope of revolution, of vertical axis, of the steam generator This envelope 10 delimits

  an enclosed interior space which is separated into a separate area

  primary and a secondary upper zone by a horizontal tube plate 12 connected from

tightly on the envelope 10.

  A vertical partition 14 divides the lower area

  primary, usually called water box,

  into an intake manifold 16 and an exhaust manifold

  cuation 18 of water circulating in the primary circuit

  of the reactor Tubing 20 and 22, welded on the

  outer cover 10 of the steam generator, connection

  tooth the collectors 16 and 18 respectively at this

primary circuit.

  An inverted U-shaped tube bundle 24 is tightly connected to the tube plate 12, in

  the upper secondary zone delimited by this

  in such a way that the two ends of each of the tubes open respectively into the collector

  intake 16 and in the exhaust manifold 18.

  The vertical branches 24 a of the tubes 24 which open into the intake manifold 16 are called hot branches and the vertical branches 24 b of the tubes 24 which open into the discharge manifold 18 are

called cold branches.

  The bundle of tubes 24 is surrounded and capped by an inner casing 26, arranged coaxially in the outer casing 10 The upper horizontal wall of this inner casing 26 opens into water / steam separators 28 surmounted by dryers 29 which communicate the space 27 provided

  inside the casing 26 with an evacuation tube

  steam cuation 30 located at the top of the envelope

  outer 10 The lower edge of the inner envelope

  lower 26 is placed at a determined distance above the tube plate 12, so as to form a passage between an annular recirculation space 32 delimited between the envelopes 10 and 26 and the space 27 delimited

in the inner envelope 26.

  Water supply to the steam generator

  secondary is carried out by a food distributor

  toric position 38 located immediately above the es

  annular recirculation space 32 A manifold

  mentation 34 tightly crosses the outer casing

  lower 10 of the steam generator and opens into the feed distributor 38 The latter can in particular be connected to the annular recirculation space 32

  by inverted J-shaped tubes 36.

  Horizontal distribution plates of

  flow 40, regularly spaced, are mounted inside

  inner envelope 26 These plates include

  attempt perforations to ensure support-

  ge of the tubes 24 of the bundle over their entire height and to achieve a radial distribution as homogeneous as possible of the secondary water flow which rises in

envelope 26.

  The lower flow distribution plate, designated by the reference 41 in FIG. 1, is located slightly above the lower edge of the inner casing 26. It is distinguished from the other plates 40 by the fact that it has a central opening. 42 of relatively large section This lower plate 41 thus makes it possible to prevent the secondary water descending through the annular recirculation space 32 from rising immediately as soon as it has crossed the lower edge of the inner envelope 26, which would have especially

  consequence of creating above the central part

  the of the tube plate 12 a static area.

  According to the invention, a deflection and purge box 44 is mounted in the space formed between the tube plate 12, the lower flow distribution plate 41 and the hot 24 a and cold 24 b branches of the tubes 24 This space, usually called water street, is designated by the reference 46 on

Figure 4.

  As illustrated in more detail in FIGS. 2 to 4, the deflection and purge box 44 extends horizontally and radially over the entire length of

  space 46, near the inner envelope

  re 26 In the embodiment illustrated in FIGS. 1 to 4, which corresponds to a steam generator of the boiler type, in which no separation is

  provided between the hot and cold branches of the tu-

  bes 24, the deflection and purge box 44 rests on the tube plate 12 by means of support studs 48 which guarantee a spacing between the bottom of the box and the upper face of the plate

with tubes.

  This spacing allows the purge orifices 50 formed in the bottom of the box 44 to drain inside this box the secondary fluid which is in the immediate vicinity of the tube plate 12 in the space 46 For this purpose, the bleed orifices open out between the support studs 48 In addition, they are advantageously more numerous and / or

  of larger section in the central part of the

  steam generator only near the outer casing

  re 10, in order to favor the drainage in this central part, in which the displacements of the fluid

secondary are the weakest.

  In addition, at least one vent 72 (FIGS. 3 and 4) is formed on the roof of the deflection box 44, in the central part of the steam generator. This vent ensures the penetration of the secondary fluid into the box 44 when the in steam generator water. As illustrated in particular in FIGS. 3 and 4, in the embodiment shown, the box

  deflection and purge 44 present in cross section

  versale a substantially rectangular shape and extends in height from the support pads 48 to a level below that of the lower flow distribution plate 41 and higher than that of the lower edge of the inner casing 26 The box 44 thus ensures a deflector function, that is to say

  that it constitutes an obstacle which opposes a flow-

  horizontal ment of the secondary fluid in a transverse direction relative to this box The deflection and purge box 44 thus fulfills the functions of homogenizing the temperature of the secondary fluid before it rises in space 27 and contributes to a good distribution of the flows of this fluid nearby

tube plate 12.

  In addition to this function, which is the same as that of the deflection or blocking devices of the prior art, there is a purge function carried out thanks to the purge orifices 50 and to drainage tubes 52 (FIG. 3) opening into the bottom of the box 44, at

  each end of it Each of the straight tubes

  swim 52 connects the box 44 to external drainage means

  laughing 54 at the steam generator, illustrated diagram

tick in figure 2.

  The drainage means 54 make it possible to pump a small quantity of secondary fluid out of the steam generator, in order to check the chemical concentrations of this fluid to maintain them at an acceptable level and to remove the suspended matter which tends to deposit in space 46 on

the tube plate 12.

  To facilitate the flow of the secondary fluid

  daire inside the deflection and purge box 44 to the drainage tubes 52, the bottom of

  box 44 forms a horizontal recovery groove

  tale 55, at the bottom of which the orifices open

  these purge 50 The groove 55 has for example, as illustrated in Figure 4, a shaped section

  of V This form can in particular be obtained by usi-

  swings from the upper face of a rail 56 forming the bottom of the box 44 and by which the latter rests on the support studs 48 The rest of the box 44 can be constituted by a plate 58 folded to form a U whose ends are welded to the lateral faces of the rail 56 The ends of the box 44 are also formed by plates welded to the plate 58 and to the rail 56 The drainage tubes 52 are welded to the latter plates, so

  to open into the bottom of the machined V on the upper side

rail 56.

  It should be noted that this particular structure

  re deflection and purge box 44 is not given

  as an example, the form and method of manufacture

  tion of this box can undergo many varian-

  your without departing from the scope of the invention.

  Thus, the substantially rectangular shape presented in section by the box 44 in the example of

  realization shown can possibly be replaced

  created by a square, triangular or other shape Furthermore, it should be noted that instead of having a constant cross section as illustrated in solid lines in FIG. 3, the box 44 can also have an evolving cross section as illustrated for example in dashed lines This evolutionary section can in particular lead to reducing

  the height of the box in the central part of the

  steam generator, compared to the height presented by this box near the inner casing 26 In this way, the efficiency of the secondary fluid withdrawals which are carried out is improved

  in the central part of space 46.

  In addition and as illustrated in particular in Figure 2, the samples in the central part of the steam generator can be further improved by adding to the deflection and purge box 44 two purge tubes 60 which are connected on each side side of the box 44, in the central part of the latter and also comprise, at the bottom, purge orifices 62 facing the plate

with tubes 12.

  The geometry of the deflection and purge box 44 is also designed to take account of the

  requirements related to maintenance operations which must

  wind can be performed on the steam generator, at the base of the tube bundle 24 Thus, as illustrated in Figure 3, the upper wall of the box 44 is located substantially at the same level as the lower edge of manholes 64 formed in the inner casing 26 of the steam generator These inspection holes 64 are themselves formed in front of inspection holes 66 provided in the outer casing 10 of the generator and normally closed by plugs (not shown) As illustrated Figure 3, the

  inspection holes 64 and 66 are located in the extension

  space 46, in order to allow operators to access between the hot and cold branches of the

beam tubes 24.

  As illustrated in Figures 5 and 6, the information

  vention is not limited to steam generators of the boiler type, but also applies to steam generators of the axial preheater type, in which a vertical separation plate 68 is disposed between the hot branches 24 a and 24 b cold tubes

  24 and connected to the tube plate 12 This connection

  ment can in particular be ensured by fitting an inverted U-shaped section 69 forming the lower edge of the separation plate 68 on a rib 13 welded on or mechanically fixed to the upper face of the plate

  with tubes 12, in the axis of the water street.

  In this case, the deflection and pur-

  ge 44 comprises two compartments 45, located on either side of the plate 68 and arranged symmetrically with respect to the latter As illustrated in FIGS. 5 and 6, these two compartments 45 can be delimited by two folded plates 70 and welded on either side of the separation plate 68, to define

two separate compartments.

  Given the separation of the two compartments 45 by the plate 68, each of them comprises, in the bottom of the box 44, purge orifices 50 whose section and / or number decreases from the center from the steam generator to its periphery. 25 As illustrated in FIGS. 5 and 6, the bottom of each of the compartments 45, in which the purge orifices 50 are made, is inclined downward in

  closer to the separation plate 68, in order to favor

  riser the drainage of the secondary fluid In addition, the roof of each of the compartments 45 is inclined upwards as it approaches the separation plate 68, in order to curve upwards the flow of secondary fluid. As seen in FIG. 6, each of the compartments 45 of the deflection and purge box communicates with drainage means (not shown) situated outside the steam generator by a separate drainage tube 52, at each of the ends of the box 44. As in the first embodiment of the invention, the roof of each of the compartments of the deflection and purge box 44 comprises, in the central part of the steam generator, at least one

  vent 72 (figure 5) ensuring penetration of the fluid

  secondary in box 44 through the bleed holes

  when filling the steam generator.

  As shown in Figure 6, the steam generator in this case has an envelope

  semi-cylindrical intermediate 74 which doubles the outside of the inner envelope 26, in the part of the latter surrounding the cold branches of the tubes 24.

  The feed toroid 38 of FIG. 1 then has a semicircular shape, in order to supply drinking water only with the space formed between the inner envelope 26 and the intermediate envelope 74 As illustrated schematically in Figure 6, the ends of the box 44 can then be closed by the intermediate casing 74. In the embodiment illustrated in Figures 5 and 6, the deflection and purge box 44 fulfills the same functions as in the first mode

  of embodiment described and moreover has the same characteristics.

Claims (7)

  1 Steam generator comprising: an outer casing (10), of vertical axis; a horizontal tube plate (12) sealingly fixed inside the outer casing; a bundle of inverted U-shaped tubes (24) comprising hot branches (24 a) and cold branches (24 b) having ends fixed on the tube plate and opening below the latter, respectively in an intake manifold (16) and in a primary fluid discharge manifold (18); an inner envelope (26) covering the bundle of tubes, a lower edge of which is spaced from the tube plate, and forming with the outer envelope an annular recirculation space (32); secondary water supply means opening into the outer casing (10), above the tube plate (12); means (28, 30) for extracting secondary steam through upper parts of the inner and outer casings; and deflection and purging means placed in a space (46) formed between the tube plate (12), the first horizontal plate (40,41) and the hot branches and the cold branches of the tubes; characterized in that the deflection and purge means comprise one (or more) deflection and purge box (44) which extends over all (or part of) the length of said space, up to near the inner casing, which extends in height up to near the lower edge of the inner casing (26), said box being spaced from the tube plate and having purge orifices (50) in look of the latter.   2 Steam generator according to claim 1, characterized in that the deflection box   tion and purge (44) extends in height up to an intermediate level between the flow distribution plate (41) and the lower edge of the inner casing (26).   3 Steam generator according to claim 2, characterized in that inspection holes (64,66) formed in the inner casing (26) and in the outer casing (10) open immediately above the ends longitudinal of the box   deflection and purge (44). 4 Steam generator according to any one of the preceding claims, characterized in that   that the deflection and purge means comprise drainage means (54) communicating with the box   deflection and purge (44) by at least one drainage tube (52) opening at at least one end of the box, at the bottom of the latter. 20 5 Steam generator according to any one of the preceding claims, characterized by the fact   that the deflection and purge means further comprise at least two purge tubes (60) opening laterally in a central part of the deflection and purge box (44), on either side of this box, and having other drain openings (62)   opposite the tube plate (12).   6 Steam generator according to any one   of the preceding claims, characterized in that   that the deflection and purge box (44) includes   a bottom forming a longitu-   dinal (55) into which the orifices of purge (50).   7 Steam generator according to any one   of the preceding claims, characterized in that   that the deflection and purge box (44) has   a uniform cross section over its entire length.   8 Steam generator according to any one   of claims 1 to 6, characterized in that   the deflection and purge box (44) has a evolving cross section.   9 Steam generator according to any one   of the preceding claims, characterized in that   that the deflection and purge box (44) rests on the tube plate (12) by means of studs   between which the drain holes (50) are formed.   Steam generator according to any one   as in claims 1 to 8, characterized by the fact   that the hot and cold branches of the tubes of the   being separated by a vertical separation plate   wedge (68) connected to the tube plate (12), the deflection and purge box (44) comprises two parts located on either side of this separation plate and supported by this plate.